1. Field of the Invention
This invention relates to the derivation of useful energy from hydrogen sulfide-containing steam, and more particularly to the reduction of the emissions of sulfur-containing compounds to the atmosphere as a result of the derivative of useful energy from steam containing both hydrogen sulfide and one or more alkaline acting components.
2. Description of the Prior Art
As conventional hydrocarbon fuel resources have become less abundant and more expensive, a worldwide emphasis has been placed on the development of alternative energy resources, such as geothermal energy resources. Electricity and other forms of useful energy can be derived from geothermal resources by producing geothermal steam and/or aqueous geothermal liquids from a subterranean geothermal reservoir and processing the produced geothermal fluid in surface facilities to extract thermal energy therefrom. Of particular interest is the generation of electricity by passing geothermal steam through a steam turbine/generator.
Most geothermal fluids contain appreciable quantities of noncondensable gases, such as hydrogen sulfide, carbon dioxide, ammonia, boric acid and the like. The presence of hydrogen sulfide in the geothermal fluid used for the derivation of useful energy often poses an environmental problem because only minute amounts of hydrogen sulfide can be acceptably discharged into the atmosphere.
Various processing methods have been proposed for the abatement of hydrogen sulfide emissions resulting from the derivation of energy from geothermal resources. One proposed method involves pretreating the motive geothermal steam to reduce the hydrogen sulfide content of the steam and then deriving useful energy from the pretreated steam. Such pretreatment methods are disclosed in U.S. Pat. Nos. 4,163,044 to Woertz and 4,123,506 to Spevak. However, these proposed pretreatment methods appear to be relatively expensive and may not result in sufficient abatement of the hydrogen sulfide emissions at a reasonable cost. It has also been proposed to treat only the noncondensable gases separated from the steam turbine effluent to remove hydrogen sulfide by means of a conventional hydrogen sulfide removal process, such as the Stretford process. These conventional processes are capable of converting very large fractions of the hydrogen sulfide in the gases treated to elemental sulfur or other useful sulfur-containing compounds. It has been found, however, that a substantial fraction of the hydrogen sulfide in the effluent from the steam turbine will not readily separate from the steam condensate with the uncondensed vapor and, as a result, this substantial fraction of hydrogen sulfide bypasses the hydrogen sulfide removal process and is eventually emitted to the atmosphere from the steam condensate. Various methods have been proposed to treat the effluent from the steam turbine and/or the steam condensate directly, such as by addition of a noncatalytic oxidant, such as hydrogen peroxide, or a catalytic oxidant, such as a ferric salt or a chelated ferric salt, to the hydrogen sulfide-containing liquid. However, these latter processes have been found to be unacceptably expensive both in terms of high chemical costs and in terms of increased corrosion and other downstream operating problems. Thus, a need exists for an economic and practical method for reducing the emissions of sulfur-containing compounds to the atmosphere resulting from the derivation of useful energy from hydrogen sulfide-containing steam.
Accordingly, a primary object of this invention is to provide a method for reducing the emission of sulfur-containing compounds to the atmosphere as a result of the derivation of useful energy from hydrogen sulfide-containing steam.
Another object of the invention is to provide a simple but effective method by which the emission of sulfur-containing compounds to the atmosphere as a result of the generation of electricity from geothermal steam is abated by means of the known, highly efficient processes for removing hydrogen sulfide from hydrogen sulfide-containing gases.
Still another object of the invention is to provide an integrated energy derivation and pollution abatement method by which useful energy can be efficiently derived from hydrogen sulfide-containing geothermal steam while substantially reducing the emission of sulfur-containing compounds to the atmosphere.
Further objects, advantages and features of the invention will become apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings.